Electrochemical Impedance Spectroscopy Excitation Through Battery Passive Balancing Circuit

Example embodiments of the present disclosure relate generally to systems, apparatuses, and methods for electrochemical impedance spectroscopy (EIS) for use with batteries, and particularly for a battery balancing circuit that may be used to generate a stimulus signal for EIS analysis of one or more batteries.

Batteries are increasingly being used in a myriad of applications, including electric vehicles, power tools, consumer electronics, and the like. These application may include many systems, such batteries with battery balancing. Many of these applications also integrate Battery Management System (BMS) integrated circuits (ICs) that monitor battery conditions and attempt to maximize the battery capacity and the lifetime, including through battery cell balancing.

Electrochemical impedance spectroscopy (EIS) may be used to generate information for determining a state of health of batteries. The state of health of a battery may indicate if a battery is healthy or aged, which may be used to prevent battery damage or determine when a battery should no longer be used. EIS may also be used to identify damage in the structure of a battery. EIS may additional be used to identify thermal drift and, consequently, potential battery explosion.

The inventors have identified numerous areas of improvement in the existing technologies and processes, which are the subjects of embodiments described herein. Through applied effort, ingenuity, and innovation, many of these deficiencies, challenges, and problems have been solved by developing solutions that are included in embodiments of the present disclosure, some examples of which are described in detail herein.

Various embodiments described herein relate to electrochemical impedance spectroscopy (EIS) for use with batteries, and particularly for a battery balancing circuit that may be used to generate a stimulus signal for EIS analysis of one or more batteries.

In accordance with some embodiments of the present disclosure, an example system is provided. The system may comprise: a plurality of battery cells, including at least a first battery cell and a second battery cell, wherein the first battery cell has a first charge and the second battery cell has a second charge; passive battery balancing circuitry configured to generate at least a first passive balancing signal to balance the first charge of the first battery cell and the second charge of the second battery cell when the first charge and the second charge are different; wherein the passive battery balancing circuitry is further configured to provide the first passive balancing signal to an EIS circuitry; wherein the EIS circuitry is configured to receive the first passive balancing signal and to provide a stimulus signal based on the first passive balancing signal to at least one of the plurality of battery cells, receive a response signal from the at least one of the plurality of battery cells based on the stimulus signal, and to generate at least one output signal based on the response signal; and a battery management system configured to receive the at least one output signal and determine at least one impedance.

In some embodiments, the passive battery balancing circuitry is further configured to passively balance each charge of each battery cell of the plurality of battery cells.

In some embodiments, the battery management system is further configured to determine a state of health of at least one of the plurality of battery cells based on the at least one impedance.

In some embodiments, to generate the at least one output signal based on the at least one response signal the EIS circuitry is further configured to synchronously acquire at least one voltage signal based on the response signal and at least one current signal based on the response signal.

In some embodiments, the at least one impedance includes at least one impedance for each of the plurality of battery cells.

In some embodiments, the passive battery balancing circuitry and the EIS circuitry are part of an integrated circuit.

In some embodiments, the at least one stimulus signal is comprised of a square wave, a triangle wave, or a sine wave.

In accordance with some embodiments of the present disclosure, an example apparatus is provided. The apparatus may comprise: passive battery balancing circuitry configured to generate at least a first passive balancing signal to balance a first charge of a first battery cell and a second charge of a second battery cell of a plurality battery cells when the first charge and the second charge are different; wherein the passive battery balancing circuitry is further configured to provide the first passive balancing signal to an EIS circuitry; wherein the EIS circuitry is configured to receive the first passive balancing signal and to provide a stimulus signal based on the first passive balancing signal to at least one of the plurality of battery cells, receive a response signal from the at least one of the plurality of battery cells based on the stimulus signal, and to generate at least one output signal based on the response signal; and a battery management system configured to receive the at least one output signal and determine at least one impedance.

In some embodiments, the passive battery balancing circuitry is further configured to passively balance each charge of each battery cell of the plurality of battery cells.

In some embodiments, the battery management system is further configured to determine a state of health of at least one of the plurality of battery cells based on the at least one impedance.

In some embodiments, to generate the at least one output signal based on the at least one response signal the EIS circuitry is further configured to synchronously acquire at least one voltage signal based on the response signal and at least one current signal based on the response signal.

In some embodiments, the at least one impedance includes at least one impedance for each of the plurality of battery cells.

In some embodiments, the passive battery balancing circuitry and the EIS circuitry are part of an integrated circuit.

In some embodiments, the at least one stimulus signal is comprised of a square wave, a triangle wave, or a sine wave.

In accordance with some embodiments of the present disclosure, an example method is provided. The method may comprise: generating, with a passive battery balancing circuitry, at least a first passive balancing signal to balance a first charge of a first battery cell and a second charge of a second battery cell of a plurality battery cells when the first charge and the second charge are different; transmitting the first passive balancing signal from the passive battery balancing circuitry to an EIS circuitry; receiving, by the EIS circuitry, at least one passive balancing signal; generating, by the EIS circuitry, at least one stimulus signal based on the at least one passive balancing signal; transmitting, by the EIS circuitry, the at least one stimulus signal to at least one of the plurality of battery cells; receiving, by the EIS circuitry, at least one response signal from the at least one of the plurality of battery cells based on the at least one stimulus signal; generating, by the EIS circuitry, at least one output signal based on the at least one response signal; and determining, by a battery management system, at least one impedance based on the at least one output signal.

In some embodiments, passively balancing, by the passive battery balancing circuitry, each charge of each battery of the plurality of battery cells.

In some embodiments, determining, by the battery management system, a state of health of at least one of the plurality of battery cells based on the at least one impedance.

In some embodiments, the at least one impedance includes at least one impedance for each of the plurality of battery cells.

In some embodiments, the passive battery balancing circuitry and the EIS circuitry are part of an integrated circuit.

In some embodiments, the at least one stimulus signal is comprised of a square wave, a triangle wave, or a sine wave.

The above summary is provided merely for purposes of summarizing some example embodiments to provide a basic understanding of some aspects of the disclosure. Accordingly, it will be appreciated that the above-described embodiments are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. It will also be appreciated that the scope of the disclosure encompasses many potential embodiments in addition to those here summarized, some of which will be further described below.

Some embodiments of the present disclosure will now be described more fully herein with reference to the accompanying drawings, in which some, but not all, embodiments of the disclosure are shown. Indeed, various embodiments of the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout.

As used herein, the term “comprising” means including but not limited to and should be interpreted in the manner it is typically used in the patent context. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of.

The phrases “in various embodiments,” “in one embodiment,” “according to one embodiment,” “in some embodiments,” and the like generally mean that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present disclosure and may be included in more than one embodiment of the present disclosure (importantly, such phrases do not necessarily refer to the same embodiment).

The word “example” or “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations.

If the specification states a component or feature “may,” “can,” “could,” “should,” “would,” “preferably,” “possibly,” “typically,” “optionally,” “for example,” “often,” or “might” (or other such language) be included or have a characteristic, that a specific component or feature is not required to be included or to have the characteristic. Such a component or feature may be optionally included in some embodiments or it may be excluded.

The use of the term “circuitry” as used herein with respect to components of a system or an apparatus should be understood to include particular hardware configured to perform the functions associated with the particular circuitry as described herein. The term “circuitry” should be understood broadly to include hardware and, in some embodiments, software for configuring the hardware. For example, in some embodiments, “circuitry” may include processing circuitry, communications circuitry, input/output circuitry, and the like. In some embodiments, other elements may provide or supplement the functionality of particular circuitry.

Various embodiments of the present disclosure are directed to improved systems, apparatuses, and methods for electrochemical impedance spectroscopy (EIS) for use with batteries, and particularly for a battery balancing circuit that may be used to generate a stimulus signal for EIS analysis of one or more batteries.

Batteries and battery balancing may be used in multiple applications, including automobiles (e.g., electric vehicles), appliances, battery storage systems, consumer electronics, and the like. In the applications battery management systems are used to monitor the health of batteries.

Battery cells may be out of balancing for one or more reasons. An imbalance between the charges of one or more battery cells may be due to differences in the internal resistances of the battery cells, each battery cell's respective capacity, battery cell temperatures, repeated charging cycles and/or discharging cycles with voltage equalization and/or ageing characteristics leading to a cell imbalances. Passive battery balancing operates on multiple battery cells (e.g., a multi-cell battery pack) by equalizing the charges on each battery cell to bring all of the multiple battery cells to the same charge level. In passive battery balancing the charge level may be to a minimum charge.

Without battery balancing, and during discharging, the battery pack may stop providing power when the lowest capacity battery cell or the overall battery capacity of the battery pack equals the lowest capacity battery cell of the battery pack. Thus an undercharged battery cell may cause the entire pack to have less power to provide or less lifetime. Additionally or alternative, without battery balancing, and during charging, a higher voltage battery cell may reach a full charge and will trip the battery pack to stop charging before lower charged battery cells are fully charged. Thus an overcharged battery cell may result in underutilization of the total potential of a battery pack.

The present disclosure provides for generating a stimulus signal to perform battery EIS from a battery balancing circuitry. In various embodiments, battery balancing circuitry may be passive battery balancing circuitry. The stimulus signal is used by EIS circuitry, which may be in a battery management system, to generate a response signal from a battery. The EIS circuitry synchronously generates a voltage signal and current signal based on the response signal. The voltage signal and the current signal are used to measure an impedance. EIS uses the impedance may be used to determine a state of health of the battery.

State of Health (SoH) indicates if a battery is healthy or aged and, thus, helps in preventing battery damage or, more simply, advising when it is time to replace a battery. SoH generally worsens over time with battery usage and charge/discharge cycles of the battery. EIS may also be used to estimate a battery's internal temperature, which may be used to identify and prevent dangerous thermal runaway. As a battery ages the impedance measurement of the second arc changes.

An exemplary embodiments includes an electric vehicle. For example, an electric vehicle may perform one or more passive balancing operations and may also, based on the passive balancing operations, excite the battery cells of the electric vehicle for measurements to be used for an EIS implementation. Various embodiments include performing EIS analysis when the battery is charging and/or discharging.

A stimulus signal generated by the passive battery balancing circuitry may be shaped by the passive battery balancing circuitry. In various embodiments, the stimulus signal may be a square wave, sine wave, triangle wave, etc. Additionally and/or alternatively, the passive battery balancing circuitry may vary the frequency of the stimulus signal. In various embodiments, the passive battery balancing circuitry may contain a plurality of FETs (e.g., MOSFETS) that may be used to shape the stimulus signal that will excite the battery. The passive battery balancing circuitry may be used to generate the stimulus signal.

Utilizing the passive battery balancing circuitry to generate the stimulus signal may provide multiple improvements, including but not limited to reducing the circuitry required to perform EIS analysis of the battery, reducing the physical footprint of the integrated circuit, and/or reducing cost. Additionally or alternatively, embodiments in accordance with the present disclosure may utilize a waveform produced by a passive battery balancing circuitry as a stimulus signal to provide to the battery. Thus, the present disclosure reuses energy associated with passive battery balancing as a stimulus signal. The energy, circuitry, and cost associated and/or required by conventional EIS systems may be reduced. This increases the efficiency of the overall system by reusing some of this lost energy to generate EIS measurements.

Passive battery balancing circuitry performs one or more operations for balancing the battery cells. In various embodiments, the passive battery balancing circuitry and EIS circuitry may be a part of a battery management system. In various embodiments, the battery management system may be on an integrated circuit.

illustrates an example battery and equivalent circuit in accordance with one or more embodiments of the present disclosure. A batteryhas a battery chemistry that is associated with an equivalent circuit comprised of a voltage source, a current, and an impedance. The impedancemay be measured based on the voltage of voltage sourceand current.

EIS measurements may be performed during both charging and discharging of a battery. A voltage measurement may be V(t) of the equivalent voltage source, which is illustrated as an open circuit voltage V. A current measurement may be I(t) of the equivalent current through an impedanceZ(jω). Measurements of the voltage V(t) and current I(t) may be used to evaluate the impedanceZ(jω) of the battery.

While batteryis illustrated as a single battery, a batterymay include multiple battery cells. An impedancemay be measured at each battery cell, all battery cells collectively, or as one or more groupings of multiple battery cells.

illustrates an exemplary EIS circuitry in accordance with one or more embodiments of the present disclosure. The EIS circuitry may comprise, among other things, an excitation circuitry, a current sensing circuitry, a voltage sensing circuitry, and a sensing resistor. The EIS circuitry may be electrically connected to at least one battery.

The EIS circuitry includes multiple analog circuitry and/or circuitry components to minimize the digital computation required. In various embodiments, the EIS circuitry also includes an EIS processor in addition to the analog circuits. The EIS processor (e.g., a MCU) may interface with a battery management system (BMS).

The EIS circuitry measures current and voltage of a response of the battery to a stimulus signal. The stimulus signal is generated by an excitation circuitry.

The excitation circuitrygenerates the stimulus signal and provides it to the batteryand a response signal is measured for both current and voltage. The voltage and current measurements may be synchronously acquired for use in generating one or more signals for generating an impedance. The current is measured across a sensing resistor, which is illustrated as RSENSE. The current is measured with current sensing circuitryto generate a current signal. The voltage is measured based on the stimulus signal and the response signal. The voltage is measured with voltage sensing circuitryto generate a voltage signal. These voltage and current measurements are used to determine impedance.

illustrates an exemplary equivalent circuitry and associated impedance measurements in accordance with one or more embodiments of the present disclosure. Various portions of a battery (e.g., chemical and/or physical portions or aspects) may have different electrical component equivalents. It will be appreciated thatis illustrative and may not be to size and/or various portions of the impedance may be associated with other models that include one or more electrical components. These different electrical component equivalents are associated with the impedance measurements. The exemplary equivalent circuitryassociated with the impedanceof a batteryvaries with frequency. For example, the equivalent circuitry of the impedance may be an inductor (L), a first resistor (R), a second resistor (R) in parallel with a first capacitor (C), a third resistor (R) in parallel with a second capacitor (C), and a resistor (R), which is referred to inwith reference number. For EIS measurements, the values of the impedance of the third resistor (R) in parallel with the second capacitor (C), which is referred to as, is used as these values change as a battery ages or is damaged.